Is a warranty deed, certified by the county treasurer, the same as a title policy?

No way. The guarantee that you receive with a warranty deed depends on the type of warranty deed that you're given. It is very rare that a seller will give you a warranty deed that guarantees everything. Usually they will only guarantee that they haven't done anything to cloud the title but they rarely guarantee anything done by prior owners. A title policy will guarantee everything.

Also, you have to remember the value of the guarantee. If you receive a warranty deed and then a problem comes up, you have to rely on the prior owner cleaning it up for you. If they don't have the time, the money or the ability to fix it you could be waiting for years. On the other hand a title company is an insurance company. They have the time, the money and the ability to fix things. If they can't fix it then they have to pay you. Getting your money back (or the value) from the prior owner could be a lot more of a problem than getting it from an insurance company.

Is a warranty deed, certified by the county treasurer, the same as a title policy?
I've never heard 'warranty deed' and 'title policy' in the same definition. A warranty deed is a type of deed received from a seller/grantor; a title policy is a type of insurance contract.